1. Field of the Invention
The invention concerns a C-arm apparatus.
2. Description of the Prior Art
C-arm apparatuses are prevalent today in medical technology. A diagnosis or treatment device is mounted on a C-shaped base body. Due to its shape, the C-arm (and with it the diagnosis or treatment device) can move orbitally around a point of a patient to be examined or treated in order to reach various angle positions between patient and diagnosis or treatment device without having to reposition the patient.
X-ray devices in which an x-ray source is mounted at one end of the C-arm and an x-ray receiver or image intensifier is mounted at the opposite end are prevalent as diagnosis apparatuses. Such an x-ray C-arm exhibits a not-insignificant dead weight.
If it is ensured in a C-arm apparatus that, given orbital travel, the diagnosis or treatment device is aligned on the same point at every angle position, this is known as an isocentric C-arm apparatus. Most notably in x-ray C-arms designed in such a way, in which the central ray of the x-ray system proceeds through the isocenter of the arrangement situated on the orbital axis (rotation axis of the orbital motion), the overall center of gravity of the arrangement naturally lies outside of the isocenter (thus radially removed from the orbital axis) due to the weight ratios. The dead weight of the overall arrangement therefore effects a torque on the C-arm. The center of gravity of the arrangement namely gravitates towards its stable equilibrium position, thus the lowest point below the orbital axis that can be reached via the orbital movement.
Force must thus be applied counter to the intrinsic angular momentum to hold the C-arm in a specific position or given movement. For example, the C-arm must be fixed in a specific position via a suitable braking device at the support device.
However, it is desirable to achieve a weight compensation at the C-arm such that the C-arm is free of force at every travel position, meaning that no torque whatsoever relative to the rotation axis acts on the C-arm. A number of approaches have previously been pursued in order to effect a weight compensation.
A first approach is to place the x-ray source and the image intensifier such that the overall center of gravity of C-arm and x-ray device lies on the rotation axis. Due to the heavy x-ray components, as compensation for the weight of the C-arm these must be further offset towards its ends. The central ray of the x-ray system then no longer proceeds through the isocenter of the arrangement, which requires a continuous re-placement of the patient region or of the entire patient to be treated by movement of the C-arm.
In a second approach the x-ray system is placed such that its central ray passes through the isocenter. Supplementary weights are additionally attached at the C-arm ends in order to again displace the overall center of gravity of the arrangement into the isocenter. However, the heavy supplementary weights significantly increase the total weight of the arrangement and mechanically load the C-arm such that it exhibits an inherent deformation.
A third approach is to act on the C-arm with brakes and an electrical motor drive such that the torque generated by gravity from the center of gravity of the C-arm is compensated by the electrical drive and the brakes. However, it is hereby a disadvantage that the C-arm requires electrical current for movement. Given a power failure a dangerous situation for the patient could occur since, for example, no access space to said patient can be achieved by movement of the C-arm.